German Patent 27 18 527, Schmid et al, assigned to the assignee of the present application, describes a metal halide high-pressure discharge lamp for general service illumination. Such lamps, adapted to be connected to alternating current standard distribution networks, for example of 110 V, 60 Hz, or 220 V, 50 Hz, with or without accessory apparatus or ballasts are well known. Lamps of this type have operationally adequate firing and operating characteristics; it has been found, however, that after some operating time--which can differ widely between individual lamps--the light output is subject to flicker, which may be rhythmical or erratic, and at random.
Flicker, as usually referred to in lamp operation, refers to changes in light intensity emitted from the lamp, which may be periodical or entirely random and aperiodical. These variations in light output or light density can be measured, and the variations are referred to as a flicker factor. Investigations have shown that there is a direct proportionality between the flicker factor and the direct voltage proportion of the lamp current. It is believed that flicker is due to insufficient electrode temperature, which manifests itself in jumps of the arc attachment on the electrode at different arcing or arc origination points.